Recent advances implicate error-prone DNA polymerases in the generation of virtually all mutations induced by environmental carcinogens in higher eukaryotic cells. These data have supported the promise of cancer chemoprevention based on the selective modulation of the activity of these proteins, based on the assumption that reducing the mutant frequency will reduce the incidence of cancer. However, carcinogenesis studies using newly-developed mouse models in which one or another of these polymerases is deficient have yielded unexpected results. Specifically, deficiency in individual polymerases may result in greatly enhanced cancer incidence in the face of reduced mutation frequencies. This unexpected result is not consistent with the somatic mutation hypothesis of carcinogenesis, and highlights the fact that there are critical gaps in our knowledge of the cellular function of this universe of polymerases. These studies have been done with ultraviolet radiation, and the role of these enzymes in mutagenesis and carcinogenesis by chemical mutagens remains largely unexplored. This application proposes to examine the hypothesis that mutagenic translesion synthesis past adducts induced in DNA by the activated form of the environmental carcinogen benzo[a]pyrene (i.e. BPDE) is dependent on the Y-family DNA polymerases eta and/or iota. This will be examined in three Specific Aims: Aim 1, To determine the frequency and spectrum of mutations induced by BPDE in the endogenous hprt gene of fibroblasts derived from isogenic strains of excision repair-deficient mice that are wild-type or combinatorially deficient in pol, eta, and/or iota. Aim 2, To examine the effect of polymerase deficiency on BPDE-induced cell cycle checkpoints, apoptosis and gene expression in these same cells. Aim 3, To examine the incidence and multiplicity of lung adenomas/adenocarcinomas induced by B[a]P in the isogenic, polymerase-deficient mice. This proposal will fill critical gaps in our knowledge of how cancer is initiated by a common environmental carcinogen. The public health implication of this work is that mutations induced by chemical carcinogens are implicated in the development of cancer, particularly lung cancer. The ultimate goal of this research is to understand how these chemicals cause cancer in order to design strategies to prevent the disease.